Radioactivity and Nuclear Equations

The densest region of an atom is the nucleus, containing protons and neutrons—collectively called nucleons.

The type of atom defined by a specific number of protons and neutrons is referred to as a nuclide. The notation for a nuclide comprises an element symbol, atomic number, and mass number.

One of several shorthand notations for nuclides uses the element name, a hyphen, and the mass number.

Nuclides with the same atomic number but different mass numbers are called isotopes of each other. Thus, carbon has three isotopes shown here.

Nuclides are also characterized by their energy state. For example, the single isotope technetium-99 exists in two different states: the lower energy ground state and a long-lived excited state called a metastable state. These two species, even though they have the same numbers of protons and neutrons, are different nuclides.

Interestingly, some elements in the periodic table have stable nuclides, which remain intact indefinitely. In contrast, some elements have only unstable nuclides, called radionuclides. For example, the spontaneous nuclear disintegration of uranium-238 produces thorium-234. The process is termed radioactive decay.

The daughter nucl